'\" t
.TH "SD_EVENT_SOURCE_SET_DESTROY_CALLBACK" "3" "" "systemd 257" "sd_event_source_set_destroy_callback"
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.SH "NAME"
sd_event_source_set_destroy_callback, sd_event_source_get_destroy_callback, sd_event_destroy_t \- Define the callback function for resource cleanup
.SH "SYNOPSIS"
.sp
.ft B
.nf
#include <systemd/sd\-event\&.h>
.fi
.ft
.HP \w'typedef\ int\ (*sd_event_destroy_t)('u
.BI "typedef int (*sd_event_destroy_t)(void\ *" "userdata" ");"
.HP \w'int\ sd_event_source_set_destroy_callback('u
.BI "int sd_event_source_set_destroy_callback(sd_event_source\ *" "source" ", sd_event_destroy_t\ " "callback" ");"
.HP \w'int\ sd_event_source_get_destroy_callback('u
.BI "int sd_event_source_get_destroy_callback(sd_event_source\ *" "source" ", sd_event_destroy_t\ *" "callback" ");"
.SH "DESCRIPTION"
.PP
\fBsd_event_source_set_destroy_callback()\fR
sets
\fIcallback\fR
as the callback function to be called right before the event source object
\fIsource\fR
is deallocated\&. The
\fIuserdata\fR
pointer from the event source object will be passed as the
\fIuserdata\fR
parameter\&. This pointer can be set by an argument to the constructor functions, see
\fBsd_event_add_io\fR(3), or directly, see
\fBsd_event_source_set_userdata\fR(3)\&. This callback function is called even if
\fIuserdata\fR
is
\fBNULL\fR\&. Note that this callback is invoked at a time where the event source object itself is already invalidated, and executing operations or taking new references to the event source object is not permissible\&.
.PP
\fBsd_event_source_get_destroy_callback()\fR
returns the current callback for
\fIsource\fR
in the
\fIcallback\fR
parameter\&.
.SH "RETURN VALUE"
.PP
On success,
\fBsd_event_source_set_destroy_callback()\fR
returns 0 or a positive integer\&. On failure, it returns a negative errno\-style error code\&.
.PP
\fBsd_event_source_get_destroy_callback()\fR
returns positive if the destroy callback function is set, 0 if not\&. On failure, returns a negative errno\-style error code\&.
.SS "Errors"
.PP
Returned errors may indicate the following problems:
.PP
\fB\-EINVAL\fR
.RS 4
The
\fIsource\fR
parameter is
\fBNULL\fR\&.
.RE
.SH "NOTES"
.PP
Functions described here are available as a shared library, which can be compiled against and linked to with the
\fBlibsystemd\fR\ \&\fBpkg-config\fR(1)
file\&.
.PP
The code described here uses
\fBgetenv\fR(3), which is declared to be not multi\-thread\-safe\&. This means that the code calling the functions described here must not call
\fBsetenv\fR(3)
from a parallel thread\&. It is recommended to only do calls to
\fBsetenv()\fR
from an early phase of the program when no other threads have been started\&.
.SH "HISTORY"
.PP
\fBsd_event_destroy_t()\fR,
\fBsd_event_source_set_destroy_callback()\fR, and
\fBsd_event_source_get_destroy_callback()\fR
were added in version 239\&.
.SH "SEE ALSO"
.PP
\fBsystemd\fR(1), \fBsd-event\fR(3), \fBsd_event_add_io\fR(3), \fBsd_event_add_time\fR(3), \fBsd_event_add_signal\fR(3), \fBsd_event_add_child\fR(3), \fBsd_event_add_inotify\fR(3), \fBsd_event_add_defer\fR(3), \fBsd_event_source_set_userdata\fR(3)
